You can withdraw from the match up until the ranking deadline passes. Contact your school administrator to initiate a withdrawal from the match.
Most match fees are non-refundable even if you withdraw later. You should not pay to access the site until you're sure you wish to participate.
Refund policies are set with the matching organization, and are posted on the website your Matching Org hosts to give you information and policies about the match. Contact your school administrator or your matching organization directly if you have more questions about refunds.